One of the byproducts of fuel combustion in an internal combustion engine is carbon particles, which are typically referred to as soot. Emission standards will typically specify a limit to the amount of soot that an engine can emit to the environment, which limit will be below the level of soot generated by the engine during operation. Therefore, various components and systems are employed by engine or vehicle manufacturers that control and limit the amount of soot emitted to the environment.
One device commonly used to limit the amount of soot expelled into the environment from an engine is referred to as a particulate trap. Such a device includes a porous substrate, for example, made of ceramic material, that may be coated with various chemical compounds that alter the composition of exhaust constituents. The porosity of the substrate acts as a filter for physically trapping carbon particles or soot in an exhaust stream passing over and/or through the filter. One can appreciate that such physical removal of carbon particles from a gas stream will progressively saturate the filter with particulate matter.
One method of restoring the performance of a particulate trap becoming saturated with soot is by a process called regeneration. Regeneration involves the oxidation or burning of accumulated particulate matter in a filter. Such oxidation may include the introduction of a combustible agent, such as fuel, onto the particulate matter to aid in the combustion. Moreover, regeneration of particulate traps often includes an elevation of the temperature of the particulate matter, for example, by elevating the temperature of the exhaust gas stream passing therethrough, prior to combustion.
Commonly used methods of regenerating a particulate filter involve an active intervention to the normal operation of the engine. Such intervention may be perceptible to an operator of the engine, and may even interfere with the normal operation of the vehicle. In other words, processes that alter the fueling strategy of an engine to introduce fuel in the exhaust stream or, more commonly, operation of the engine to increase exhaust temperature, can alter the behavior and power output of a vehicle or machine. Such alterations may interfere with normal use of equipment, which can have repercussions in the uptime and cost of operating the equipment.
The time and duration of a regeneration event depends on many factors, such as the extent of accumulation of soot or carbon particulate matter on the filter, the operating conditions of the engine, and so forth. One example of a particulate trap system and control method therefor can be seen in U.S. Pat. No. 7,406,822 (hereafter, the '822 patent), which issued to Funke et al. and is assigned Caterpillar Inc. of Peoria, Ill. The '822 patent describes a system that includes a particulate trap and a regeneration device configured to reduce an amount of particulate matter in the particulate trap.
The system described in the '822 patent further includes a controller that activates the regeneration device in response to the first to occur of at least three trigger conditions. The trigger conditions may include, for example, operation of the engine for a predetermined period, consumption of a predetermined amount of fuel by the engine, detection of an elevated backpressure upstream of the particulate trap, detection of a pressure differential across the particulate trap that exceeds a threshold, or a calculated amount of particulate matter accumulated on the particulate trap that exceeds a limit. Such parameters may be independently evaluated to determine that a regeneration event is required. Thereafter, the controller may activate the regeneration device to oxidize the particulate matter found at the particulate trap.
Even though activation of a regeneration event for a particulate trap, whether such event involves use of a regeneration device or not, can be effective in removing trapped particulate matter when such concentration on a trap has exceeded a limit. Such regeneration may occur at any time during operation of the engine and may reduce, even temporarily, the effectiveness of any machine or vehicle, which heretofore has been an undesirable but necessary process. For example, a particulate trap installed on an on-highway truck may require the truck to be stopped on the side of the road while a regeneration event is taking place. It is desired to reduce or eliminate such intrusions to the normal operation of a vehicle or machine whenever possible.